| | Montezuma, IA | Marengo, IA | United States |
| Population | 1,337 | 2,714 | 329,725,481 |
| Female Population | 46.1% | 53.7% | 50.5% |
| Male Population | 53.9% | 46.3% | 49.5% |
| Median Age | 37.9 | 41.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,454 | 2,531 | 309,327,143 |
| Population - 2000 | 1,440 | 2,535 | 285,036,114 |
| Population - 1990 | 1,651 | 2,270 | 251,960,433 |
| Pop. 2000 to Now | -3.6% | -2.7% | 15.6% |
| Pop. 1990 to Now | -15.9% | 8.6% | 30.8% |
| space4 | | | |
| Population Density | 538.9 | 1,283.2 | 93.4 |
| Land Area | 2.5 | 2.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Montezuma, IA | Marengo, IA | United States |
| Age 0 to 4 | 7.7% | 4.9% | 5.9% |
| Age 5 to 9 | 4.8% | 4.8% | 6.1% |
| Age 10 to 14 | 7.7% | 8.5% | 6.6% |
| Age 15 to 17 | 1.7% | 4.9% | 3.9% |
| Age 18 to 20 | 5.6% | 1.6% | 4.0% |
| Age 21 to 24 | 4.5% | 4.3% | 5.2% |
| Age 25 to 34 | 16.2% | 11.2% | 13.8% |
| Age 35 to 44 | 7.4% | 14.5% | 12.9% |
| Age 45 to 54 | 12.9% | 10.2% | 12.6% |
| Age 55 to 59 | 7.3% | 8.5% | 6.7% |
| Age 60 to 64 | 10.6% | 6.5% | 6.3% |
| Age 65 to 74 | 8.1% | 13.6% | 9.6% |
| Age 75 to 84 | 2.7% | 4.4% | 4.5% |
| Age 85 and over | 2.8% | 2.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Montezuma, IA | Marengo, IA | United States |
| White | 93.6% | 94.0% | 59.4% |
| Black | 0.4% | 0.3% | 12.2% |
| Asian | 0.3% | 0.3% | 5.6% |
| Native American | 0.4% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 3.7% | 2.0% | 3.2% |
| Hispanic | 1.6% | 3.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Montezuma, IA | Marengo, IA | United States |
| Married Population | 55.7% | 49.5% | 49.8% |
| Currently Married | 52.6% | 48.9% | 48.0% |
| Married but Separated | 3.1% | 0.6% | 1.8% |
| Single Population | 44.3% | 50.5% | 50.2% |
| Never Married | 23.7% | 26.7% | 33.8% |
| Divorced | 13.4% | 17.4% | 10.8% |
| Widowed | 7.2% | 6.5% | 5.6% |
| space5 | | | |
| Household Size | 2.26 | 2.38 | 2.60 |
| Households | 579 | 1,112 | 124,010,992 |
| Family Households | 346 | 637 | 80,755,759 |
| Married couple, w/children | 31.5% | 31.1% | 30.5% |
| Married couple, no children | 40.5% | 46.0% | 42.9% |
| Non Family Households | 233 | 475 | 43,255,233 |
| Single householder, w/children | 9.5% | 16.2% | 15.8% |
| Single householder, no children | 18.5% | 6.8% | 10.8% |